Diagnostic utility of the aberrant immunohistochemical expression of CD3 molecules for peripheral T-cell lymphomas

The histological diagnosis of peripheral T-cell lymphomas (PTCLs) is often challenging. Flow cytometry (FCM) sometimes shows the loss of pan-T-cell markers for PTCLs, suggesting the neoplastic nature of these cells. Immunohistochemically, the total loss of pan-T-cell markers has been demonstrated in PTCLs. Furthermore, except for the total loss, the aberrant immunohistochemical expressions of pan-T-cell markers have also been empirically observed in PTCLs, but the details remain unexamined. Therefore, the present study semi-quantitatively evaluated the aberrant expression of cytoplasmic CD3ε (cCD3ε), the most common immunohistochemical pan-T-cell marker, in 91 PTCL cases. The expressions of the other CD3 molecules, CD3δ, CD3γ, and CD3ζ were also examined. Frequencies of the total immunohistochemical loss of CD3 molecules and loss of surface CD3ε (sCD3ε) in FCM were analyzed for comparison. The results showed atypical, aberrant expression patterns for immunohistochemical CD3 molecules: perinuclear, cytoplasmic, membranous, and partial negative. The frequency of each molecule was as follows: cCD3ε 40.7 %, CD3δ 26.4 %, CD3γ 53.8 %, and CD3ζ 54.9 %, especially the latter two showed high frequency in peripheral T-cell lymphoma, not otherwise specified, angioimmunoblastic T-cell lymphoma, and adult T-cell lymphoma/leukemia. Immunohistochemical total loss was less than aberrant expression in all CD3 molecules, with the frequency of cCD3ε being the lowest (6.6 %). The loss of sCD3ε in FCM was observed in 43.3 % of cases, with a similar frequency to the aberrant expression of cCD3ε. In conclusion, the aberrant immunohistochemical expression of cCD3ε was a useful finding as is sCD3ε loss in FCM, but CD3γ and CD3ζ were more useful, facilitating the diagnosis of PTCLs.